A computer-based sound synthesis and analysis system developed in this Section was used to present natural sequences of the "chuck" vocalization to group-housed squirrel monkeys. No significant behavioral changes except for "chuck" responses were made by the group. This suggests that the only message communicated by individual "chuck" calls is the presence and identity of the vocalizer. In contrast, loud calls such as the marmoset "phee" produce obvious behavioral changes in the listener to occasional vocal responses. Thus, primate vocalizations that broadcast over long distances, dur to their loudness and other acoustic properties, induce changes in the arousal level or emotional state of the listener, whereas vocalizations that carry only a few meters, due to their softness, induce no clear changes in the arousal level or emotional state of the listener. It is these latter vocalizations that are the most likely candidates to be instruments for social learning in primate social groups. The role of experience in mediated agonistic vocal recruitment was examined in a free-ranging group of 35 rhesus macaques at the Poolesville field station. Juvenile males were found to use recruit,ent calls to enlist the aid of other family members, indicating that vocal recruitment is not restricted to female members of macaque matrilines.